I'm of the oppinion that there really aren't any registry cleaners you can trust 100%. Cccleaner comes closer than most, but it has the occasional hiccup. My thoughts on the matter are if you are to the point where you are experiancing registry errors, its time for a complete reload rather than risking destabilizing your entire registry.

Piriform ccleaner is good as the others have said, it also comes with other nifty features, such as the ability to securely delete files from your computer using a 7 pass algorithm. It even lets you do that for all the free space of your drive, sodeleted files can't be recovered, should you have a need to hide the **** from a girlfriend or something, haha.